Burying seedlings to the true leaves

I am slightly confused over this. Some people here thinks that you can do this with all veg and others only with solanceas (Tomatoes, chilies and peppers). Can some cast some light on this for me. If you could to this with beans, marrows, courgettes that could be great as the ones I am raising indoors are going a bit leggy

As jude5 says, none of the Cucurbitaceae family ought to be planted deeper than their root-ball. Courgettes are a no-no. On the other hand, tomatoes, peppers and their related plants benefit from a deeper hole as they will form additional roots from the stem to aid nutrient assimilation